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"But overall the benefits to kea populations from pest control continue to outweigh the loss of individual birds to 1080."

The repellent used, d-pulegone, had shown promise in previous trials but was not effective enough to prevent kea deaths in this field operation, she said.

Once all the data had been fully analysed DOC would review its options, which included increasing the repellent concentration and investigating other repellents. Analysis of the baits had subsequently shown that the repellent was less than the target concentration.

Ms Crowell said further work was needed to account for dissipation during bait storage.

The repellent was used over 10,619ha around Otira as well as in a nearby Tb Free New Zealand operation over 10,130ha in the Taipo Valley undertaken, from June 26 to August 1.

Kea are particularly inquisitive and DOC has been researching ways to minimise the loss of individual kea in 1080 operations.

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DOC has been working with the Kea Conservation Trust, Tb Free NZ and Landcare Research over a number of years to develop a repellent to prevent kea deaths during aerial 1080 operations. This has included research trials in pens, aviaries and field sites to test whether the repellents work, are safe and do not affect possum and rat control. The current research is funded by DOC, Tb Free and the Ministry of Business, Innovation and Employment.

A new baiting protocol was introduced in 2010 to reduce the risk to kea, which included using less palatable baits and avoiding open areas above the bush line.

DOC has been investigating two bird repellents, including d-pulegone, a food additive based on the peppermint flavour found in some plants in the mint family.

Since 2008, 155 kea have been monitored through ten 1080 operations, with 20 (12.9 per cent) recorded fatalities, DOC says.